1. Field of the Invention
The present invention relates to a device for preventing a high voltage transformer of a microwave oven from being overheated, which directly senses a temperature in a second coil of the high voltage transformer of the microwave oven and thereby supplies or cuts off power to the transformer according to the temperature.
2. Prior Art
A microwave oven is a cooker for heating food by a high frequency electric field, which includes a heating chamber and a machine chamber. In the microwave oven, a magnetron and a high voltage transformer are disposed in the machine chamber. The high voltage transformer applies a high voltage to the magnetron to make the magnetron generate ultra microwaves, and the magnetron irradiates the ultra microwaves into the heating chamber so as to activate molecular movements in the food put in the heating chamber, so that the food is heated.
In the meantime, the high voltage transformer has a large quantity of coils which generate a large quantity of heat when the transformer is operated. Accordingly, the operation efficiency of the microwave oven is lowered and components of the microwave oven can be damaged when the machine chamber is overheated due to the heat generated from the coils. Further, there is a possibility of danger that the microwave oven will catch a fire.
Therefore, proper means for preventing a high voltage transformer of a microwave oven from being overheated when operated has been required, and particularly International Electrotechnical Commission (IEC) regulates that the temperature of the high voltage transformer of the microwave oven should not be over 210 Celsius degree.
FIG. 5 is a circuit diagram of a conventional device for preventing the temperature in the machine chamber of a microwave oven from being over-elevated as described above. As shown, a high voltage transformer T1 has a first coil L1 to which an alternating current voltage is applied, and a second coil L2 at which a circuit including L5 a high voltage fuse F1, a high voltage condenser C1, a high voltage diode D1, and a magnetron M1 is constructed.
In the device for preventing machine chamber of a microwave oven from being overheated as described above, high voltage fuse F1 is cut off or high voltage diode D1 is shorted before high voltage fuse F1 is cut off, when an overcurrent flows through the second circuit L2. When high voltage diode D1 is shorted before high voltage fuse F1 is cut off, a closed loop comprising second coil L2, high voltage fuse F1, high voltage condenser C1, and high voltage diode D1 is constructed. At this moment, a large quantity of currents abruptly flow in this closed loop, and thereby high voltage fuse F1 is cut off.
When high voltage fuse F1 is cut off, power supply to second coil L2 of high voltage transformer T1 is ceased so as to prevent transformer F1 from being overheated and accordingly catching a fire, and at the same time the operation of magnetron M1 is stopped.
However, in the conventional device for preventing a high voltage transformer of a microwave oven from being overheated having the above-described construction, the temperature of the high voltage transformer is not directly sensed but indirectly preestimated through the electric currents flowing therethrough, and accordingly there is a disadvantage that the temperature of the high voltage transformer is not prevented precisely and efficiently from being over-elevated and there is a possibility of danger that the electric current can be cut off by a current over-inflowing through the fuse, even when the high voltage transformer is not overheated. Further, in the conventional device, whenever the high voltage diode is shorted and/or the high voltage fuse is cut off, these damaged components, which are very expensive, must be replaced with new ones to operate the transformer again, and thereby the maintenance expense is relatively very high.